Mehtod and apparatus for modifying object with electrons generated from cold cathode electron emitter

ABSTRACT

Apparatus and method for modifying an object with electrons are provided, by which the object can be uniformly and efficiently modified with the electrons under a pressure substantially equal to atmospheric pressure even when having a relatively wide surface area to be treated. This method uses a cold-cathode electron emitter having the capability of emitting electrons from a planar electron emitting portion according to tunnel effect, and preferably comprising a pair of electrodes, and a strong field drift layer including nanocrystalline silicon disposed between the electrodes. The object is exposed to electrons emitted from the planar electron emitting portion by applying a voltage between the electrodes. It is preferred that an energy of the emitted electrons is selected from a range of 1 eV to 50 keV, and preferably 1 eV to 100 eV.

TECHNICAL FIELD

The present invention relates to method and apparatus for modifying anobject with electrons.

BACKGROUND ART

In the past, electron irradiation has been utilized to surface modify,sterilize or clean an object. For example, Japanese Patent EarlyPublication [kokai] No. 2002-6094 discloses an electron irradiatingapparatus that can be used to form a cross-bridge structure or purifyexhaust gas. This apparatus is provided with an electron gun having ahot filament, high-voltage power source for supplying an electriccurrent to the hot filament to generate electrons, acceleratingelectrode for accelerating the generated electrons to obtain an electronbeam, and an electromagnet for deflecting the electron beam.

However, since the hot filament is an electron source having a spot-likeor linear electron emitting portion, it is needed to scan the electronbeam to modify a relatively wide surface area of the object. This leadsto a reduction in treatment efficiency, and a complication in devicestructure. In addition, since the hot filament is heated under a highdegree of vacuum to generate the electrons, vacuum equipments such asdecompression chamber and vacuum pump are needed. As a result, there isa problem that the application area of the apparatus is narrow despitean increase in cost of the apparatus.

On the other hand, Japanese Patent Early Publication No. 3-29662discloses a method of sterilizing animal feeding stuff by irradiation ofa high energy electron beam of 5 to 10 MeV. In addition, Japanese PatentEarly Publication No. 2000-69908 discloses a method of sterilizing greentea powder by irradiation of an electron bean of 200 keV to 300 keV. Inthese methods, since an expensive electron accelerator is needed toobtain the high energy electron beam, a considerable increase in cost ofthe apparatus becomes a problem. In addition, it has been difficult toirradiate such a high electron beam to a wide surface area of the objectat a time.

SUNNARY OF THE INVENTION

In view of the above-mentioned problems, a concern of the presentinvention is to provide a method of efficiently and uniformly modifyingan object with electrons even when the object has a relatively widesurface area to be modified.

That is, the method of the present invention comprises the steps ofproviding a cold-cathode electron emitter, which has the capability ofemitting electrons from a planar electron emitting portion according totunnel effect, applying a voltage to the emitter to emit the electronsfrom the planar electron emitting portion, and exposing the object tothe emitted electrons. As the cold-cathode electron emitter, it isparticularly preferred to use a Ballistic electron Surface-emittingDevice (BSD) comprising a pair of electrodes, and a strong field driftlayer including nanocrystalline silicon disposed between the electrodes.

According to the present invention, since the cold cathode electronemitter that is a planar-type electron emitting source is used, it ispossible to perform the modifying treatment to the object under areduced pressure near atmospheric pressure in addition to theimprovement in treatment efficiency and uniformity. In particular, whenusing the BSD as the cold cathode electron emitter, it is possible toperform the modifying treatment under the atmospheric pressure withoutusing vacuum equipments such as a vacuum pump and decompression chamber.Therefore, there are many advantages of an expansion of the applicationarea, downsizing of the apparatus, and a reduction in cost of themodifying treatment.

In the present invention, the meaning of the word “modify” or“modifying” includes various types of reactions such as hardening,polymerization, decomposition, bridging, oxidizing, ionization,excitation and radical reaction, changing surface tension, surfaceenergy, wettability, adhesion, absorption index, refractive index orcrystal structure, introduction of defects, sterilization, disinfection,filtration of virus, mold, pollen and so on, physiological actions suchas germination, ageing or prevention maturation, propagation of goodbacteria, deodorizing, cleaning, purifying, and removal of harmfulsubstances.

In the above method, it is preferred that an energy of the electronsused to modify the object is selected from a range of 1 eV to 50 keV,and preferably 1˜100 eV.

A further concern of the present invention is to provide an apparatusfor efficiently and uniformly modifying an object with electrons. Thatis, this apparatus comprises a cold-cathode electron emitter, which hasthe capability of emitting electrons from a planar electron emittingportion according to tunnel effect, voltage applying unit for applying avoltage to the emitter to emit the electrons from the planar electronemitting portion, and a case for accommodating the emitter therein. Thecase has an opening, through which the electrons or a gas activated bythe electrons are provided. From the same reason as the above, it isparticularly preferred to use a Ballistic electron Surface-emittingDevice (BSD) as the cold-cathode electron emitter, which comprises apair of first and second electrodes, and a strong field drift layerincluding nanocrystalline silicon disposed between the first and secondelectrodes.

In addition, it is preferred that the above apparatus further comprisesan accelerating electrode positioned in face-to-face relation with theplanar electron emitting portion to accelerate the electrons. In thiscase, it is possible to control the energy of electrons irradiated tothe object.

In the above apparatus, it is preferred that the first electrode iscomposed of an array of first electrode strips, which are arranged to bespaced from each other in a lateral direction, and the second electrodeis composed of an array of second electrode strips, which are arrangedto be spaced from each other in a direction intersecting with thelateral direction, wherein the electrons are selectively emitted fromthe planar electron emitting portion corresponding to an intersectingregion(s) between at least one of the first electrode strips and atleast one of the second electrode strips when the voltage is appliedtherebetween by the voltage applying unit. Furthermore, it is preferredthat the apparatus has an first selector for selecting at least one ofthe first electrode strips, and a second selector for selecting at leastone of the second electrode strips, wherein the voltage applying unitapplies the voltage between at least one of the first electrode stripsselected by the first selector and at least one of the second electrodestrips selected by the second selector to selectively emit the electronsfrom the planar electron emitting portion corresponding to theintersecting region(s) therebetween. In this case, it is possible tochange a modification area depending on the size of the object, therebyachieving energy saving and reducing the modification cost.

Another concern of the present invention is to provide an apparatus forperforming the modifying method described above. This apparatuscomprises a cold-cathode electron emitter, which has the capability ofemitting electrons from a planar electron emitting portion according totunnel effect, voltage applying unit for applying a voltage to theemitter to emit the electrons from the planar electron emitting portion,and a holder for supporting the object such that the object is exposedto the emitted electrons. From the same reason as the above, it isparticularly preferred to use the BSD as the cold-cathode electronemitter.

These and still other objects and advantages of the present inventionwill become more apparent from the best mode for carrying out theinvention, referring to the attached drawings.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an apparatus for modifyingan object with electrons according to a first embodiment of the presentinvention;

FIG. 2 is a schematic perspective view of a cold cathode electronemitter of the apparatus;

FIG. 3 is a schematic perspective view of another cold cathode electronemitter;

FIG. 4 is an explanatory view of a strong-field drift layer of the coldcathode electron emitter;

FIG. 5 is a graph showing energy distributions of electrons emitted fromthe cold cathode electron emitter;

FIG. 6 is a schematic cross-sectional view of an apparatus according toa modification of the first embodiment;

FIGS. 7A and 7B are schematic perspective views of preferredarrangements of cold cathode electron emitters;

FIG. 8 is a schematic cross-sectional view of an apparatus according toa further modification of the first embodiment;

FIG. 9 is a schematic cross-sectional view of an apparatus according toanother modification of the first embodiment;

FIG. 10 is a schematic cross-sectional view of an apparatus formodifying an object with electrons according to a second embodiment ofthe present invention;

FIG. 11 is a schematic cross-sectional view of an apparatus according toa first modification of the second embodiment;

FIG. 12 is a schematic cross-sectional view of an apparatus according toa second modification of the second embodiment;

FIG. 13 is a schematic cross-sectional view of an apparatus according toa third modification of the second embodiment;

FIG. 14 is a schematic cross-sectional view of an apparatus according toa fourth modification of the second embodiment;

FIG. 15 is a schematic cross-sectional view of an apparatus formodifying a gas object with electrons according to a third embodiment ofthe present invention;

FIG. 16 is a schematic cross-sectional view of an apparatus formodifying a liquid object according to a modification of the thirdembodiment;

FIG. 17 is a schematic cross-sectional view of an apparatus formodifying a sold object according to a further modification of the thirdembodiment;

FIGS. 18A and 18B are top and cross-sectional views of an apparatus formodifying an object with electrons according to a fourth embodiment ofthe present invention;

FIG. 19 is a schematic cross-sectional view showing a method ofmodifying an object with electrons according to a fifth embodiment ofthe present invention; and

FIG. 20 is a schematic cross-sectional view showing a modifyingtreatment according to a modification of the fifth embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is explained below in detail according topreferred embodiments.

First Embodiment

As shown in FIGS. 1 and 2, an apparatus for modifying an object 2 withelectrons according to the present embodiment comprises a cold cathodeelectron emitter 1 having a planar electron emitting portion 10, avoltage applying unit 30 for applying a voltage to the emitter to emitelectrons from the planar electron emitting portion, a case 20 foraccommodating the emitter therein, which is made of an insulatingmaterial and has an opening 21 used to provide the emitted electrons tothe outside of the case, and a holder 40 for supporting the object 2such that the object is exposed to the electrons provided through theopening. In FIG. 1, the numeral 50 designates a mesh electrode attachedto the opening 21 to accelerate the electrons generated from the emitter1. Alternatively, a window member made of a material, through which theelectrons can pass, may be attached to the opening in place of theaccelerating electrode.

As shown in FIG. 2, the cold cathode electron emitter 1 comprises aconductive substrate 14 such as n-type silicon, a non-dopedpolycrystalline silicon layer 13 formed on a top surface of theconductive substrate 14, strong-field drift layer 12 formed on thepolycrystalline silicon layer 13, a first electrode 11 provided on thestrong-field drift layer 12, and an ohmic electrode 15 formed on thebottom surface of the conductive substrate 14. In this case, theconductive substrate 14 and the ohmic electrode 15 function as a secondelectrode. In addition, a top surface of the first electrode 11 providesthe planar electron emitting portion 10 of the emitter 1. Thestrong-field drift layer 12 may be directly formed on the conductivesubstrate not through the polycrystalline silicon layer 13.Alternatively, another cold cathode electron emitter 1 shown in FIG. 3may be used, which is characterized in that an insulating substrate 16such as glass or a ceramic material is used in place of the conductivesubstrate 14, an electrode layer 17 is formed as the second electrode onthe insulating substrate, and the strong-field drift layer 12 is formedon the electrode layer 17. The cold cathode electron emitter 1 used inthis embodiment is known as Ballistic electron Surface-emitting Device(BSD).

As shown in FIG. 4, the strong field drift layer 12 is composed ofcolumnar polycrystalline silicon grains 100 extending toward the firstelectrode 11, first silicon oxide thin films 110 formed in surfaces ofthe silicon grains 100, fine grains of nanocrystalline silicon 120formed between the adjacent silicon grains 110, and second silicon oxidethin films 130 formed in surfaces of the fine grains 120, each of whichhas a smaller thickness than a crystal grain size of the nanocrystallinesilicon.

For example, the strong field drift layer 12 can be produced accordingto the following procedures. Firstly, a nanocrystallization process isperformed to a non-doped polycrystalline silicon layer on a conductivesubstrate, thereby obtaining a nanocrystalline composite layer havingthe columnar polycrystalline silicon grains 100 and the fine grains ofnanocrystalline silicon 120. In the nanocrystallization process, forexample, an electrolytic solution obtained by mixing a 55 wt %hydrofluoric aqueous solution with ethanol at a mixing ratio of 1:1 isused.

Then, the conductive substrate having an electrode layer used as theohmic electrode and the polycrystalline silicon layer is placed in theelectrolytic solution. The electrode layer is used as anode electrode,and a platinum electrode positioned on the polycrystalline silicon layeris used as cathode electrode. By supplying a constant electric currenthaving a current density of 12 mA/cm² between the anode and cathodeelectrodes for a predetermined time period, e.g., 10 seconds, whileirradiating light from a 500 W tungsten lamp, the nanocrystallinecomposite layer can be obtained. In the nanocrystalline composite layer,amorphous silicon may be formed at regions other than the silicon grains100 and the fine grains of nanocrystalline silicon 120. Alternatively,depending on the condition of the nanocrystalline process, the amorphoussilicon regions may be formed by fine pores. In this case, thenanocrystalline composite layer has a porous structure.

Next, an oxidizing process is performed to the nanocrystalline compositelayer to obtain the strong field drift layer 12. In this oxidizingprocess, for example, an electrolytic solution obtained by adding 0.04mol/l of potassium nitrate into an organic solvent such asethyleneglycol is used. Then, the conductive substrate having thenanocrystalline composite layer is placed in the electrolytic solution.The electrode layer used as the ohmic electrode is the anode electrode,and a platinum electrode positioned on the nanocrystalline compositelayer is used as cathode electrode. By supplying a constant electriccurrent having a current density of 0.1 mA/cm² between the anode andcathode electrodes for a time period needed for a voltage increase of 20V therebetween, the nanocrystalline composite layer can beelectrochemically oxidized to obtain the strong field drift layer 12.

In the strong field drift layer 12, amorphous silicon or apartially-oxidized amorphous silicon may be formed at regions other thanthe silicon grains 100, the fine grains of nanocrystalline silicon 120,the first and second silicon oxide thin films (110, 130). When formingthese silicon oxide thin films (110, 130), a nitriding process or anoxynitriding process may be performed in place of the oxidizing processdescribed above. In the case of the nitriding process, those siliconoxide thin films are replaced by silicon nitride thin films. In the caseof the oxynitriding process, those silicon oxide thin films are replacedby silicon oxynitride thin films.

To emit electrons from the cold cathode electron emitter 1, when arequired voltage is applied between the first electrode 1 1 and theohmic electrode 15 such that an electric potential of the firstelectrode is higher than the electric potential of the ohmic electrode,electrons are injected from the second electrode into the strong fielddrift layer 12. At this time, since most of the electric field isimpressed to the first and second silicon oxide thin films (110, 130) ofthe strong field drift layer 12, the injected electrons are acceleratedby the strong electric field impressed to those silicon oxide thinfilms, so that the electrons are drifted in regions between the silicongrains 100 of the strong field drift layer 12, as shown by the arrows inFIG. 4, and emitted outside through the first electrode 11 without beingalmost scattered by the fine grains of nanocrystalline silicon 120. Thisphenomenon is called as Ballistic electron Surface-emitting phenomenonthat is a kind of the tunnel effect. Since heat generated from thestrong field drift layer 12 is released through the silicon grains 100,it is possible to avoid the occurrence of popping at the time of theelectron emission.

Electrons emitted from the cold cathode electron emitter 1 is called ascold electrons. On the contrary, electrons generated from a spot-like orlinear electron emitter such as hot filament by heating is called asthermal electrons. In addition, the cold cathode electron emitter 1 usedin the present invention is known as an field-emission type electronsource that is preferably used for display devices, for example, asdisclosed in Japanese Patent Early Publication No. 2000-100316.

The electrons provided from the cold cathode electron emitter 1 throughthe opening 21 of the case 20 are irradiated to a surface to be modifiedof the object 2 supported by the holder 40. An energy of the electronsirradiated can be determined according to the purpose of the modifyingtreatment. For example, to avoid radio activation of the object, it ispreferred to use the energy less than 10 MeV, and more preferably lessthan 1 MeV. In the case of using the energy smaller than 300 keV, aradiological protection equipment for X-ray can be simplified.

To achieve desired modifying effects that meet the purpose of thepresent invention, it is preferred to use electrons having an energyselected from a range of 1 to 50 keV, and particularly 1 to 100 eV. Whenirradiating the electrons having the energy of approximately 4 eV, atomsand molecules can be excited. In addition, when irradiating theelectrons having an energy of 4 to 12 eV, which is equal to or slightlylarger than 4 to 8 eV of the bonding energy between atoms, the objectcan be effectively surface modified. When irradiating the electronshaving an energy of 20 to 100 eV, atoms and molecules can be ionized.Furthermore, when irradiating the electrons having an energy smallerthan the ionization energy to a gas containing moisture or steam as theobject, the electrons are attached to the object, so that minus ions canbe readily generated.

By the way, there is an advantage that the energy level of the electronsemitted from the cold cathode electron emitter is higher in proportionto a magnitude of the voltage applied between the electrodes. Forexample, electrons having an energy of 1 eV to several ten electronvolts can be obtained by use of 10 to 20 V of the applied voltage, whichis much higher than the electron level, e.g., 0.1 eV, of the thermalelectrons generated from the hot filament.

As an example, energy distributions of electrons emitted from the coldcathode electron emitter 1 are shown in FIG. 5. In this figure, “A”, “B”and “C” designate profiles showing the energy distributions obtainedwhen the voltages of 12 V, 14V and 16V are respectively applied betweenthe electrodes. These profiles show that as the applied voltageincreases, the peak becomes sharper, and the peak position is shifted tothe high energy side.

In the case of controlling the energy of the electrons emitted from thecold cathode electron emitter 1, it is preferred to dispose anaccelerating electrode 50 above the first electrode 11 in the vicinityof the opening 21 of the case 20, and apply a required voltage betweenthe accelerating electrode and the first electrode such that an electricpotential of the accelerating electrode is higher than the electricpotential of the first electrode. For example, as shown in FIG. 3, whena voltage Vps is applied between the first and second electrodes (11,17) of the cold cathode electron emitter 1, and an acceleration voltageVc is applied between the accelerating electrode (anode electrode) 50and the first electrode 11 such that the electric potential of theaccelerating electrode is higher than the electric potential of thefirst electrode, it is possible to control the energy of the emittedelectrons depending on a magnitude of the acceleration voltage Vc.

In FIG. 3, when an electric current flowing between the first and secondelectrodes (11, 17) is represented as a diode current Ips, and anelectric current flowing between the accelerating electrode 50 and thefirst electrode 1 1 is represented as an emission current Ie, anelectron emissivity can be defined as a rate of the emission current Ieto the diode current Ips (=Ie/Ips). As this ratio is larger, theelectron emissivity increases. According to the present invention, evenwhen a relatively low voltage of 10 to 20 V is applied as the voltageVps between the first and second electrodes (11, 17), it is possible toemit the electrons. In addition, since the dependence of the electronemissivity on degree of vacuum is small, and popping does not happen atthe time of electron emission, it is possible to stably emit theelectrons at an improved electron emissivity. This means that electronscan be emitted at a pressure in the vicinity of atmospheric pressure. Asthe voltage Vps, a constant DC voltage or a pulse voltage can be used.In the case of using the pulse voltage, a reverse-bias voltage may beapplied when the voltage Vps is not applied. Similarly, as theacceleration voltage Vc, a constant DC voltage or a pulse voltage can beused.

The accelerating electrode 50 can be made of a metal material such asaluminum, tungsten and stainless steel. In addition, the acceleratingelectrode 50 may be configured in a frame shape to fit the opening 21 ofthe case 20. In this case, the electrons are irradiated to the objectthrough an inner space of the frame shape of the accelerating electrode.Alternatively, a grid electrode may be disposed in the vicinity of theopening of the case.

In conclusion, the modifying apparatus and method of this embodimentpresents the following effects.

-   (1) Since the cold cathode electron emitter having the planar    electron emitting portion is used, it is possible to uniformly    irradiate electrons to a wide surface area of the object at a time,    as compared with the case of using an electron emitting source    having a spot-like or linear electron emitting portion such as hot    filament. As a result, improved modification efficiency and    uniformity can be achieved.-   (2) The cold cathode electron emitter such as BSD has the capability    of emitting electrons under atmospheric pressure. Therefore, it is    possible to perform the modifying treatment without using vacuum    equipments such as decompression chamber and vacuum pump.-   (3) The cold cathode electron emitter can be driven by a pulse    voltage because a rise time needed to emit the electrons is shorter    than the electron emitting source for emitting thermal electrons    such as hot filament. Therefore, there is an advantage of saving    power consumption.-   (4) Since no device for scanning the electron beam is needed in the    present invention, a reduction in cost of the apparatus can be    achieved.

As a modification of this embodiment, as shown in FIG. 6, it ispreferred that a pair of cold-cathode electron emitters 1, each of whichis the cold-cathode electron emitter explained above, are disposed suchthat electrons are emitted in opposite two directions through a pair ofopenings 21 formed in the case 20. In this case, the second electrodes17 of the pair of cold-cathode electron emitters are respectivelyconnected to opposite surfaces of the insulating substrate 16, as shownin FIG. 7A Alternatively, it is preferred that the ohmic electrodes 15of the pair of cold-cathode electron emitters are composed of a commonelectrode disposed between strong field drift layers 12, as shown inFIG. 7B In this case, electrons are emitted in opposite two directionsby applying a voltage between the common electrode 15 and the firstelectrodes 11 of the cold-cathode electron emitters. Therefore, it ispossible to simplify the voltage applying unit by reducing the number ofelectrodes.

In addition, by forming a two or three dimensional array of at least onecold cathode electron emitter having the capability of simultaneouslyemitting the electrons in the opposite two directions, as shown in FIG.7A or 7B, and at least one cold cathode electron emitter having thecapability of emitting the electrons in one direction, as shown in FIG.2 or 3i it is possible to design a high-efficiency modifying apparatusfor simultaneously irradiating electrons to the object from differentdirections. For example, a modifying apparatus shown in FIG. 8 has apair of treatment spaces, in each of which electrons can besimultaneously irradiated from the opposite two directions. In FIG. 8,the numeral 72 designates a gas supply unit for supplying a gas as theobject into the case. Therefore, the gas activated by the electrons inthe treatment spaces is ejected outside through the opening 21 of thecase 20.

A modifying apparatus according to a modification of this embodiment isshown in FIG. 9. This apparatus is characterized by comprising a holder40 for supporting the object 2, and an emitter traveling unit 60 fortraveling the case 20 with the cold cathode electron emitter 1 thereinaround the object. As the emitter traveling unit, for example, it ispreferred that a rail 61 is formed along a desired trajectory, and acarrier 63 for the case 20 is traveled along the rail. In this case, itis possible to selectively irradiate the electrons to a desired surfacearea of the object, without moving the object, and also change theirradiation angle of the electrons to the object.

The emitter traveling unit 60 may further comprise a distance adjusterfor moving the case 20 upward or downward against the carrier 63 toadjust the distance between the cold cathode electron emitter 1 and theobject 2. In addition the holder 40 may be rotatable around the holderaxis, if necessary. When it is needed to perform the modifying treatmentin a desired gas atmosphere, it is preferred that the above-describedmodifying apparatus is accommodated in a chamber with a gas supply unitfor charging the gas into the chamber. In the present invention, sincethe modifying treatment can be performed under atmospheric pressure, thestructure of the chamber can be simplified as compared with the case offorming a decompression chamber. The emitter traveling unit 60 and thegas supply unit can be controlled by use of an operation panel providedoutside of the chamber.

Second Embodiment

In this embodiment, apparatus and method for modifying a gas as theobject by irradiation of electrons are explained.

As shown in FIG. 10, the modifying apparatus of this embodiment ischaracterized by comprising a case 20 having a gas inlet 22 forsupplying the object gas into the case, and an opening 21 for providinga modified gas to the outside, and an acceleration electrode (anodeelectrode) 50 disposed in a face-to-face manner with an electronemitting portion 10 of a cold cathode electron emitter 1 in the case.The cold cathode electron emitter is the same as the emitter used in thefirst embodiment. Therefore, duplicate explanation is omitted. To avoidthe influence of humidity on electron emitting efficiency of the coldcathode electron emitter, it is preferred that the gas supplied in thecase 20 through the gas inlet 22 is a dry gas having a low moisturecontent. For example, it is preferred that the relative humidity (RH %)is smaller than 30%, and more preferably 10%. In the case, electronsemitted from the cold cathode electron emitter 1 are accelerated towardthe acceleration electrode 50, and irradiated to the gas existing in aspace between the cold cathode electron emitter and the accelerationelectrode to ionize the gas. As a result, the ionized gas is providedoutside through the opening 21.

For example, negative ions can be readily generated by supplying the drygas containing an element having positive electron affinity or a largeelectron affinity such as oxygen in the case 20 through the gas inlet21. In this case, it is preferred to apply an acceleration voltage Vc ofseveral volts to several ten volts between the acceleration electrode 50and the first electrode 11. The generated negative ions provided throughthe opening 21 are bonded with molecules in the outside air to generatevarious sorts of ions. On the other hand, when a voltage of several tenvolts to several mega volts, which is larger than the ionization energy(for example, several ten electron volts) of the dry gas, is appliedbetween the acceleration electrode 50 and the first electrode 11,positive ions can be generated.

It is also preferred that an auxiliary electrode (not shown) is placedoutside of the case 20 in front of the opening 21 to control the amountsof ions ejected therefrom. In the case of ejecting the negative ionsfrom the opening 21, it is preferred that an electric potential of theauxiliary electrode is determined to be higher than the electricpotential of the first electrode 11 of the cold cathode electron emitter1. In addition, as shown in FIG. 1 1, a pair of auxiliary electrodes(55, 56) may be disposed in the case 20 such that one of the auxiliaryelectrodes 55 is positioned adjacent to the cold cathode electronemitter 1 and at the side of the opening 21, and the other auxiliaryelectrode 56 is positioned adjacent to the acceleration electrode 50 atthe side of the opening. In this case, it is preferred that an electricpotential of the auxiliary electrodes (55, 56) is determined to behigher than the first electrode 11 of the cold cathode electron emitter1 to eject the negative ions from the opening 21.

The structure of the auxiliary electrode is not specifically limited.For example, the auxiliary electrode comprises a mesh electrode, gridelectrode, electrode obtained by concentrically arranging ring-likeelectrode members having different diameters, and an electrode obtainedby arranging a plurality of linear electrode members in parallel witheach other. In addition, the modifying apparatus may comprise a sprayunit for spraying a second gas containing liquid particles such asmedical constituents or steam to the ions ejected through the opening 21of the case 20. In this case, the second gas can be ionized by the ionsprovided from the cases.

A modifying apparatus according to a modification of this embodiment isshown in FIG. 12. This apparatus is characterized by using a case 20having air inlets 22 for supplying a low moisture gas such as dried air,oxygen or an inert gas in the case, which are formed in opposite sidewalls of the case, and an opening 21 for ejecting the electrons emittedfrom the cold cathode electron emitter 1 and the gas modified by theelectrons, which is formed in a top wall of the case 20 and above theelectron emitting portion 10 of the cold cathode electron emitter 1.

To control the energy of the electrons ejected from the opening 21, asshown in FIG. 13, an acceleration electrode (anode electrode) 50 havinga ring shape can be disposed above the opening of the case 20. Ifnecessary, an auxiliary electrode 55 such as mesh electrode may beattached to an inner surface of the top wall of the case 20 around theopening 21. In this case, it is preferred that an electric potential ofthe auxiliary electrode 55 is determined to be higher than the electricpotential of the first electrode 11 of the cold cathode electron emitter1, and the electric potential of the accelerating electrode 50 isdetermined to be higher than the electric potential of the auxiliaryelectrode 55. The electrons emitted from the cold cathode electronemitter 1 are accelerated by the accelerating electrode 50 and theauxiliary electrode 55, and then irradiated to the object 2 supported bythe holder 40 through a center opening of the accelerating electrode.

Alternatively, the auxiliary electrode 55, e.g., mesh electrode may bedisposed between the electron emitting portion 10 of the cold cathodeelectron emitter 1 and the accelerating electrode 50 attached to aninner surface of the top wall of the case 20, as shown in FIG. 14. Inthis case, a gas supplied from gas inlets 22 in the case 20 is modifiedby electrons emitted from the cold cathode electron emitter 1, and thenthe modified gas is ejected outside from a pair of openings 21 formed inupper portions of opposite side walls of the case 20.

Third Embodiment

In this embodiment, modifying apparatus and method for irradiatingelectrons to a gas or a gas containing liquid particles such as steam ormoisture are explained.

That is, as shown in FIG. 15, this modifying apparatus is characterizedby using a case 20 comprising gas inlets 22 for supplying a gas into thecase, which are formed in lower portions of side walls of the case, andan opening 21 for ejecting electrons emitted from the cold cathodeelectron emitter 1, which is formed in a top wall at a position facingthe electron emitting portion 10 of the cold cathode electron emitterplaced on a bottom wall of the case. In addition, this apparatus has anaccelerating electrode SO disposed above the opening, and a gas flowchannel 70 provided on the top wall of the case 20. In this case, thegas is supplied as the object to the gas flow channel 70 from a gassupply unit 72, as shown by the horizontal arrow in FIG. 15, and thenmodified by the electrons accelerated from the cold cathode electronemitter 1 toward the acceleration electrode 50 through the opening 21.In addition, an auxiliary electrode 55 configured in a ring shape isattached to the inner surface of the top wall of the case around theopening 21. It is preferred that an electric potential of the auxiliaryelectrode 55 is determined to be higher than the electric potential ofthe first electrode 11 of the cold cathode electron emitter 1, and anelectric potential of the accelerating electrode 50 is determined to behigher than the electric potential of the auxiliary electrode 55.

In this embodiment, it is preferred that the gas supplied in the case 20through the gas inlet 22 is a gas composed of atoms or molecules havinga smaller electron affinity than oxygen. For example, such a gascomprises helium, argon, xenon, and nitrogen. In this case, the electronemitted from the cold cathode electron emitter 1 can be efficientlyprovided to the gas flowing in the gas flow channel 70. In other words,when the air is charged in the case 20, the number of electrons having asufficient energy for achieving the purpose of the modifying treatmentmay decrease, or variations in energy distribution of the electrons mayincrease because of interference of the electrons emitted from the coldcathode electron emitter with atoms and molecules in the air. Due tothis reason, when the air is charged in the case, it is preferred thatthe gas flow channel 70 is spaced from the electron emitting portion 10of the cold cathode electron emitter 1 by a distance of 5 mm to 1 cm toperform the modifying treatment.

On the other hand, when the gas having a smaller electron affinity thanoxygen is charged in the case 20, the gas flow channel 70 can be spacedfrom the electron emitting portion 10 by a larger distance of several cmto several ten cm. As a result, it leads to an improvement in modifyingefficiency and a higher degree of freedom of designing the apparatus. Inaddition, it is possible to prevent contamination of the cold cathodeelectron emitter 1, and prolong the maintenance cycle. The gas suppliedinto the gas flow channel 70 may contain medical constituents as theliquid particles.

As a modification of this embodiment, in the case of irradiatingelectrons to a liquid as the object, it is preferred that the coldcathode electron emitter 1 is disposed on the inner surface of the topwall of the case 20, and electrons emitted downwardly from the coldcathode electron emitter are irradiated to the liquid through theopening 21 formed in the bottom wall of the case, as shown in FIG. 16.In FIG. 16, the numeral 80 designates a liquid flow channel disposedunder the case 20. The liquid is supplied to the liquid flow channel 80by a liquid supply unit 82. In addition, by replacing the liquid flowchannel 80 with a conveyer 90 such as a belt conveyer, as shown in FIG.17, it is possible to successively modify solid objects on the conveyer90 by the irradiation of electrons.

Fourth Embodiment

In this embodiment, a modifying apparatus having the capability ofchanging an electron irradiation area depending on the size of theobject is explained. That is, as shown in FIGS. 18A and 18B, the firstelectrode 11 of the cold cathode electron emitter 1 is composed of anarray of first electrode strips X1 to X8, which are arranged to bespaced from each other in a lateral direction. On the other hand, thesecond electrode 17 of the cold cathode electron emitter is composed ofan array of second electrode strips Y1 to Y8, which are arranged to bespaced from each other in a direction intersecting with said lateraldirection. Therefore, the strong field drift layer 12 is disposedbetween the array of first electrode strips X1 to X8 and the array ofsecond electrode strips Y1 to Y8.

In this case, when the voltage is applied between at least one of thefirst electrode strips X1 to X8 and at least one of the second electrodestrips Y1 to Y8 by the voltage applying unit, the electrons areselectively emitted from an intersecting region(s) therebetween. Forexample, as shown in FIG. 18A, when the voltage is applied between thefirst electrode strips X1, X2 and the second electrode strips Y2, Y3,electrons are emitted from the intersecting region R1. In addition, whenthe voltage is applied between the first electrode strips X4, X6 and thesecond electrode strips Y4, Y6, electrons are emitted from pluralintersecting regions R2. Thus, the modifying apparatus of thisembodiment is suitable to efficiently perform the modifying treatment tothe object having regions, which the irradiation of electrons is notneeded. In addition, there is an advantage of saving power consumption.

To readily change the electron irradiation area, it is preferred thatthe modifying apparatus further comprises a first selector for selectingat least one of the first electrode strips X1 to X8, and a secondselector for selecting at least one of the second electrode strips Y1 toY8, and a controller for controlling the voltage applying unit inresponse to outputs of the first and second selectors. In this case, thecontroller controls the voltage applying unit such that the voltage isapplied between at least one of the first electrode strips X1 to X8selected by the first selector and at least one of the second electrodestrips Y1 to Y8 selected by the second selector to selectively generatethe electrons from the intersecting region(s) therebetween.

Fifth Embodiment

This embodiment explains about a modifying treatment performed under acondition that an object 2 directly contacts an electron emittingportion 10 of the cold cathode electron emitter 1. As shown in FIG. 19,the object 2 is directly placed on an electron emitting surface of thecold cathode electron emitter, and then electrons are irradiated to theobject by the cold cathode electron emitter. In this case, as comparedwith a case that the object is spaced from the cold cathode electronemitter by a required distance, it is possible to minimize interferencebetween the electrons emitted from the cold cathode electron emitter andatoms or molecules existing in the space therebetween. As a result,variations in energy distribution of electrons irradiated to the objectcan be reduced to uniformly perform the modifying treatment.

In addition, it is preferred that the whole object 2 is positioned in anelectron penetrating region Rp, which is defined over a distance in anormal direction to the electron emitting surface of the cold cathodeelectron emitter 1. The distance is determined such that the electronsemitted from the cold cathode electron emitter 1 can pass through theobject 2 placed in the electron penetrating region Rp. For example, whenthe object is a liquid or solid, it is preferred that the distance issmaller than 1 mm. In addition, when the object is a gas, it ispreferred that the distance is smaller than 10 cm. As described below,this method is useful to activate the inside as well as the surface ofthe object by the irradiation of electrons.

As shown in FIG. 20, the object 2 made of a catalyst material isdisposed on the cold cathode electron emitter 1 such that a bottomsurface of the object directly contacts the electron emitting surfacethereof. On the other hand, the top surface of the object is exposed toa gas flow channel 70. Electrons are emitted to the object 2 by coldcathode electron emitter 1 to activate the catalyst material. When apolluted gas such as exhaust gas is supplied into the gas flow channel70 by a gas supply unit 72, it is cleaned by the activated catalystmaterial. This method can be also utilized to generate hydrogen frommethanol or methane. In place of the catalyst material, a biomaterial,or a polymer membrane may be used as the object 2.

In the above embodiments, a Metal-Insulator-Metal (MIM) electron emitteror a Metal-Insulator-Semiconductor (MIS) electron emitter may be used asthe cold cathode electron emitter in place of the Ballistic electronSurface-emitting Device (BSD).

In addition, the apparatus explained in each of the above embodimentscan be regarded as the minimum unit in the case of constructing a highperformance modifying apparatus, which has the capability of providing afurther improved treatment efficiency. For example, such a highperformance apparatus can be obtained by forming a two- orthree-dimensional array of a plurality of modifying apparatuses, each ofwhich is substantially the same as the apparatus of any one of the aboveembodiments, such that object is exposed to larger amounts of electronsprovided from different directions.

In addition, the modifying apparatus according to any one of the aboveembodiments may comprise a sensor for detecting the presence or absenceof the object in the treatment space, and a switching device(s) forapplying the voltage between the first and second electrodes and ifnecessary between the accelerating electrode and the first electrode inaccordance with an output of this sensor. Moreover, the switchingdevice(s) may be operated according to the output of another sensor fordetecting information such as amounts or the number of the object(s),posture or position of the object, or the kind of the object.Furthermore, the modifying apparatus may comprise means for controllingparameters such as irradiation amount, irradiation time, and irradiationangle as well as the energy level of electrons, thereby improving themodifying effect and saving power consumption

EXAMPLES

Some examples of demonstrating modifying effects achieved by use of themodifying apparatuses described above of the present invention areintroduced below.

Example 1

In this Example, the modifying apparatus shown in FIG. 10 was used. Byapplying 15 V to the cold cathode electron emitter 1, and 100 V to theaccelerating electrode 50, while supplying oxygen gas into the case 20through the gas inlet 22 under atmospheric pressure, negative ions ofoxygen were ejected outside through the opening 21 without theoccurrence of ozone. By use of the generated negative ions of oxygen, arefreshing effect to the human body and a propagation of good bacteriasuch as yeast and acidophilus were confirmed. This effect can be alsoutilized to propagate a Bacterium coli carrying a useful gene inbiological and medical fields.

Example 2

In this Example, the modifying apparatus shown in FIG. 11 was used. Byapplying 15 V to the cold cathode electron emitter 1, 100 V to theaccelerating electrode 50, and 300 V between the auxiliary electrodes(55, 56), while supplying oxygen gas into the case 20 through the gasinlet 22 under atmospheric pressure, negative ions of oxygen wereejected outside through the opening 21 without the occurrence of ozone.In this case, amounts of the generated negative ions were larger thanthe amounts generated in Example 1. By use of the generated negativeions of oxygen, a refreshing effect to the human body and a furtherincrease in propagation of good bacteria were confirmed.

Example 3

In this Example, the modifying apparatus shown in FIG. 15 was used. Byapplying 15 V to the cold cathode electron emitter 1, 500 V to theaccelerating electrode 50, and 300 V to the auxiliary electrode 55,while supplying a dry air into the case 20 through the gas inlet 22, andflowing a gas including steam provided from the gas supply unit 72 inthe gas flow channel 70 under atmospheric pressure, negative ions ofoxygen and minus ion clusters each having an aggregation of watermolecules with a diameter of 10 to 20 nm as a nucleus were ejectedwithout the occurrence of ozone from a gas outlet the gas flow channel70 provided at the side opposed to the gas supply unit 72. By use of thegenerated negative ions of oxygen and the minus ion clusters, antifungalaction, antibacterial action, and inactivation of pollen were confirmed.In addition, the indoor air was deodorized and cleaned.

Example 4

In this Example, the modifying apparatus shown in FIG. 13 was used. Byapplying 15 V to the cold cathode electron emitter 1, 1000 V to theaccelerating electrode 50, and 300 V to the auxiliary electrode 55,while supplying a dry air into the case 20 through the gas inlet 22under atmospheric pressure, electrons were irradiated to an agar mediumcarrying Bacterium coli thereon as the object 2 through the opening 21.As compared with the case of not irradiating electrons, amounts ofcolonies of Bacterium coli were remarkably decreased by the irradiationof electrons. Thus, a high bactericidal effect was confirmed.

INDUSTRIAL APPLICABILITY

From understood from the above embodiments, according to the presentinvention, it is possible to uniformly and efficiently perform variouskinds of modifying treatments depending on the energy level of electronsirradiated to the object even when the object is in a liquid or gasstate other than the solid state, or an organism. In addition, by usingthe cold cathode electron emitter comprising the pair of electrodes, andthe strong field drift layer including nanocrystalline silicon disposedbetween the electrodes, i.e., the Ballistic electron Surface-emittingDevice (BSD), the modifying treatments can be performed underatmospheric pressure.

Therefore, the modifying apparatus and method of the present inventionare expected to be used in a large variety of application areas such assmoke neutralizer, air conditioner, humidifier, dehumidifier, clothdrier, dish drier, lavatory drier, fan heater, cleaner, refrigerator,closet, kitchen cabinet, shoe cupboard, bath room, laundry machine,freezer, ice maker, and sterilizer.

1. A method of modifying an object with electrons comprising the stepsof: providing a cold-cathode electron emitter, which has the capabilityof emitting electrons from a planar electron emitting portion accordingto tunnel effect; applying a voltage to said emitter to emit theelectrons from said planar electron emitting portion; and exposing theobject to the electrons.
 2. The method as set forth in claim 1, whereinsaid emitter comprises a pair of electrodes, and a strong field driftlayer including nanocrystalline silicon disposed between saidelectrodes, and wherein the electrons are emitted from said planarelectron emitting portion by applying the voltage between saidelectrodes.
 3. The method as set forth in claim 1, wherein the object isexposed to the electrons under a pressure substantially equal toatmospheric pressure.
 4. The method as set forth in claim 1, comprisingthe steps of accelerating the electrons emitted from said emitter toirradiate the accelerated electrons to the object.
 5. The method as setforth in claim 1, wherein an energy of the electrons is in a range of 1eV to 50 keV.
 6. The method as set forth in claim 5, wherein the energyof the electrons is in a range of 1 eV to 100 eV.
 7. The method as setforth in claim 1, wherein the object is a dry gas.
 8. The method as setforth in claim 7, wherein said dry gas includes at least one of oxygenand nitrogen.
 9. The method as set forth in claim 1, wherein a gashaving a smaller electron affinity than oxygen is filled in a spacebetween said emitter and said object.
 10. The method as set forth inclaim 1, wherein said object is placed to directly contact said planarelectron emitting portion of said emitter.
 11. An apparatus formodifying an object with electrons comprising: a cold-cathode electronemitter, which has the capability of emitting electrons from a planarelectron emitting portion according to tunnel effect; voltage applyingmeans for applying a voltage to said emitter to emit the electrons fromsaid planar electron emitting portion; and a case for accommodating saidemitter therein, said case having an opening, through which theelectrons or a gas activated by the electrons are provided.
 12. Theapparatus as set forth in claim 11, wherein said cold-cathode electronemitter comprises a pair of first and second electrodes, and a strongfield drift layer including nanocrystalline silicon disposed between thefirst and second electrodes, and wherein said voltage applying meansapplies the voltage between the first and second electrodes to emit theelectrons from said planar electron emitting portion.
 13. The apparatusas set forth in claim 11, further comprising a holder for supporting theobject at outside of said case such that the electrons are irradiated tothe object through said opening.
 14. The apparatus as set forth in claim11, wherein said case has an intake port for supplying a gas as theobject therein, so that said gas is activated in said case by theelectrons, and then provided outside through said opening.
 15. Theapparatus as set forth in claim 12, wherein said cold-cathode electronemitter is provided with a pair of cold-cathode electron emittersdisposed in said case such that the electrons are provided in oppositetwo directions through a pair of openings formed in said case when thevoltage is applied between the first electrodes and the secondelectrodes of said emitters by said voltage applying means.
 16. Theapparatus as set forth in claim 11, further comprising an acceleratingelectrode for accelerating the electrons emitted from said emitter,which is positioned in face-to-face relation with said planar electronemitting portion.
 17. The apparatus as set forth in claim 16, whereinsaid accelerating electrode is an anode electrode, and a gas suppliedinto a clearance between said case and said anode electrode is activatedby the electrons provided through said opening.
 18. The apparatus as setforth in claim 12, wherein the first electrode is composed of an arrayof first electrode strips, which are arranged to be spaced from eachother in a lateral direction, and the second electrode is composed of anarray of second electrode strips, which are arranged to be spaced fromeach other in a direction intersecting with said lateral direction,wherein the electrons are selectively emitted from said planar electronemitting portion corresponding to an intersecting region(s) between atleast one of the first electrode strips and at least one of the secondelectrode strips when the voltage is applied therebetween by saidvoltage applying means.
 19. The apparatus as set forth in claim 18further comprising an first selector for selecting at least one of thefirst electrode strips, and a second selector for selecting at least oneof the second electrode strips, wherein said voltage applying meansapplies the voltage between at least one of the first electrode stripsselected by the first selector and at least one of the second electrodestrips selected by the second selector to selectively emit the electronsfrom said planar electron emitting portion corresponding to theintersecting region(s) therebetween.
 20. An apparatus for modifying anobject with electron comprising: a cold-cathode electron emitter, whichhas the capability of emitting electrons from a planar electron emittingportion according to tunnel effect; voltage applying means for applyinga voltage to said emitter to emit the electrons from said planarelectron emitting portion; and a holder for supporting the object suchthat the object is exposed to the electrons.
 21. The apparatus as setforth in claim 20, wherein said cold-cathode electron emitter comprisesa pair of electrodes, and a strong field drift layer includingnanocrystalline silicon disposed between said electrodes, and whereinthe voltage applying means applies the voltage between said electrodesto emit the electrons from said planar electron emitting portion.